1. Field of the Invention
The present invention relates to an electrophotographic image forming apparatus that forms an electrostatic latent image on an electrophotographic photosensitive member through an electrophotographic process, and visualizes the electrostatic latent image with a developer contained in a developing device, and more particularly, to an electrophotographic image forming apparatus having developer amount detecting means capable of sequentially detecting the remaining amount of developer contained in a developer containing portion, a process cartridge and a developing device.
The electrophotographic image forming apparatus is directed to, for example, an electrophotographic copying machine, an electrophotographic printer such as an LED printer or a laser beam printer, an electrophotographic facsimile machine and an electrophotographic word processor.
The process cartridge makes at least one of charging means, developing means and cleaning means and an electrophotographic photosensitive member integrally into a cartridge that is detachably mountable to a main body of the electrophotographic image forming apparatus, or makes at least the developing means and the electrophotographic photosensitive member integrally into a cartridge that is detachably mountable to a main body of the electrophotographic image forming apparatus.
2. Related Background Art
Up to now, in an image forming apparatus using an electrophotographic image forming process, there has been applied a process cartridge system that makes the electrophotographic photosensitive member and process means that acts on the electrophotographic photosensitive member into a cartridge that is detachably mountable to a main body of the electrophotographic image forming apparatus. The process cartridge system can remarkably improve the operability, since the maintenance of the apparatus can be conducted by a user per se not depending on a service man. For that reason, the process cartridge system has been widely employed in the electrophotographic image forming apparatus.
One type of the electrophotographic image forming apparatuses of the above process cartridge system includes a developer amount presence and absence detecting device that informs the user of a fact that the developer has been completely consumed.
The details will be further described. FIG. 18 shows an example of an image forming apparatus A to which a conventional process cartridge B is mounted. A developing device 10 that constitutes developing means in the process cartridge B, includes a developer container 11 having a developing portion 13 that supplies a developer T to a latent image formed on a photosensitive drum 1 serving as an image bearing member to visualize the latent image and a hopper portion 14 provided for the purpose of reserving and storing the developer T. Then, the developer T within the hopper portion 14 is fed to the developing portion 13 from the interior of the hopper portion 14 by the gravity and an agitating device 15 or the other developer feeding means.
In the developing portion 13, a developing roller 12 that serves as a cylindrical developer bearing member for feeding the developer T up to a developing position opposite to the photosensitive drum 1 is disposed in the vicinity of the photosensitive drum 1. The developer T is stuck and held on the surface of the developing roller 12, and the developer T is fed up to the developing position opposite to the photosensitive drum 1 by the rotation of the developing roller 12.
The amount and height of the developer T are regulated and uniformly coated on the developing roller 12 by developer regulating means 17 such as a doctor blade while the developer T is being fed. The developer T is rubbed by the developing roller 12, the developer regulating means 17 or the developer T per se so that the developer T is charged during a process where the developer T is fed onto the developing roller 12.
Then, the developer T fed to a portion of the developing roller 12 opposite to the photosensitive drum 1 by the developing roller 12, that is, to a developing position, is transferred onto the photosensitive drum 1 by an appropriate developing bias voltage applied between the photosensitive drum 1 and the developing roller 12 by a developing bias power supply 54 that serves as bias applying means, and an electrostatic latent image on the photosensitive drum 1 is then developed to form a toner image.
The developer T that has not been used for development is fed while it remains on the developing roller 12, and then again contained in the developing portion 13.
On the other hand, a recording medium P set in a sheet feeding cassette 20 is conveyed to a transfer position by a pickup roller 21 and conveying means 22 having a conveying roller pair, a registration roller (not shown) and so on in synchronism with the formation of the toner image. A transfer roller 4 is disposed as transfer means at the transfer position, and the toner image on the photosensitive drum 1 is transferred onto the recording medium P by application of a voltage.
The recording medium P to which the toner image has been transferred is conveyed to fixing means 5 by a conveying guide 23. The fixing means 5 includes a driving roller 5c and a fixing roller 5a having a heater 5b therein which applies a heat and a pressure to the recording medium P which is passing through the fixing means 5 to fix the transferred toner image onto the recording medium P. Thereafter, the recording medium P is externally discharged from the apparatus.
The photosensitive drum 1 after the toner image thereon has been transferred onto the recording medium P by the transfer roller 4, is subjected to a succeeding image forming process after the developer remaining on the photosensitive drum 1 has been removed by cleaning means 6. The cleaning means 6 scrapes off the residual developer on the photosensitive drum 1 by an elastic cleaning blade 7 disposed so as to be abutted against the photosensitive drum 1 and collects the residual developer into a waste developer reservoir 8.
As described above, in the developing device 10, because the developer T is consumed every time the developing operation is repeated, it is necessary to monitor the presence and absence of the developer T in the developing portion 13 at any time so as to prevent the shortage of the developer T.
Under the above circumstances, the conventional developing device 10 includes a developer amount detecting device as means for detecting the residual amount of the developer, and the developer amount detecting device includes an antenna electrode 18 for detection of the residual amount of the developer, which is disposed horizontally in the interior of the developing portion 13 in order to detect the residual amount of the developer T.
The developer amount detecting device further includes a developer amount measuring circuit 50 which is equipped with a capacitance detecting circuit 52 as means for measuring a capacitance between the antenna electrode 18 and the developing roller 12. The capacitance detecting circuit 52 is connected with the antenna electrode 18. With this structure, the developing bias voltage which is applied to the developing roller 12 by the developing bias power supply 54 is detected by the antenna electrode 18 to measure the capacitance between the antenna electrode 18 and the developing roller 12.
The developer amount measuring circuit 50 also includes a reference capacitance 53 as means for setting a capacitance that is a reference for comparison and a capacitance detecting circuit 51 as means for measuring the reference capacitance 53. The reference capacitance 53 and the developing bias power supply 54 are connected to each other, and the developing bias voltage is detected through the reference capacitance 53, to thereby obtain the capacitance that is a reference in measurement of an unknown capacitance.
The developer amount detecting device compares an output of the capacitance detecting circuit 52 with an output of the capacitance detecting circuit 51 for the reference capacitance by a comparing circuit 55 serving as comparing means to detect a difference therebetween, and judges the depletion of developer T by a developer amount warning circuit 57 to notify a user that the developer T is little, if the difference is lower than a given value.
As described above, in the conventional image forming apparatus, the antenna electrode 18 for detection of the residual amount of developer T is disposed in the developing portion 13, and in the detecting method, a time immediately before the developer is emptied, can be accurately detected.
On the contrary, if the residual amount of developer T within the developer container can be sequentially detected, the user can be notified of a state in which the developer within the developer container is consumed. Therefore, the user can prepare a new process cartridge for a replacement timing.
In view of the above, in order to sequentially detect the residual amount of developer T, there has been proposed a method of counting a number of prints and a method in which a period of time of producing a light emission signal to a laser or the like which forms the electrostatic latent image is integrated so as to sequentially grasp the residual amount of developer T. However, in the conventional method, there is a fear that an error becomes large due to a variation of the consumed amount of toner caused by the fluctuation of environments where the apparatus is employed or a variation of the printing ratio of the print image.